A lighting circuit of a metal halide discharge lamp or the like is known for use in a vehicular illuminating light source. The lamp includes a direct current voltage booster circuit having a DC-DC converter, a direct current-alternating current converting circuit, and a starting circuit. For example, in one arrangement, the starting circuit includes a transformer whose primary side is provided with a capacitor (starter capacitor), and a self-break down type switching element of a spark gap or the like. The self-break down type switching element conducts when a terminal voltage exceeds a threshold by charging the capacitor. A starting pulse (or starter pulse) can be generated by causing a primary current flow in the transformer to be applied to the discharge lamp from a secondary winding of the transformer.
Some arrangements include a circuit for storing energy by charging the capacitor, which has an auxiliary winding for generating a high voltage at the transformer so as to supply a voltage from the auxiliary winding to a capacitor by way of a rectifying element of a diode or the like.
According to the foregoing circuit arrangement, a problem can arise by magnetically coupling a main winding (primary winding and secondary winding) of the transformer and the auxiliary winding for generating the high voltage through a core. In particular, when the high voltage pulse is generated at the primary winding of the transformer to start the discharge lamp, a surge voltage in accordance with the pulse generation also is generated at the auxiliary winding. When the energy is stored by the starter capacitor, the starting signal is attenuated and results in deterioration of the starting performance.
Hence, it would be desirable to guarantee starting performance of a discharge lamp lighting circuit without a significant increase in size and cost.